1. Field of the Invention
The present invention relates to a method for shutting off a projector having a fan and a light source. More particularly, the present invention relates to a method capable of shortening time needed to shut off a projector without affecting lifetime of the projector.
2. Description of Related Art
In order to provide dynamic image with high brightness and high contrast ratio, high power light sources are utilized in conventional projectors. With the increase in power of the light source, heat generated in the projectors may increase. Therefore, cooling fans are usually utilized to lower the temperature of the projector, so as to prevent the operating temperature of the projector from being too high. Aside from maintaining the operating temperature of projectors during projection, the cooling fans also play an important role in shutting off projectors.
When a projector is shut off, light sources and fans thereof may be turned off immediately. When the fans are turned off immediately, the heat dissipating condition is worse than that during normal operation since the residue heat in the projector still exits. Therefore, the temperature of the projector may arise to higher than the operating temperature and then cool down to room temperature. The temperature variation is generally called “over-shooting”. The light source and other electronic devices of the projector may be damaged and the lifetime of the projector may be reduced because of the “over-shooting” phenomenon.
As shown in FIG. 1, when a projector is turned on (t1), a light source and a cooling fan may be turned on simultaneously and run continuously for a period of time. When the projector is shut off, the light source is turned off first (t2) and the cooling fan may run continuously in a period of time (from t2 to t3) so as to dissipate heat in the projector (so-called cooling mode). Generally, the cooling mode continues about 1-2 minutes (from t2 to t3) such that the light source is cooled down to a temperature lower than the re-lighting temperature and the projector is capable of being turned on again. Then, the power source can be disconnected by user and the projector can be stored immediately. The re-lighting temperature described herein is defined as a minimum temperature which ensures that the light source can be restarted. In the cooling mode mentioned above, user can not disconnect the power source until the light source is cooled down by the cooling fan completely such that the time needed to shut off a projector is too long for a user, who may want to store the project rapidly after clicking the shut down button, to be satisfied.